There has been many previous solar collector systems described which provide energy savings particularly for meeting heating or hot water requirements. Although such systems have been known for some time, their implementation has been inhibited by the high cost of solar collector units and the relatively lower cost of common fossil fuels. With the cost of all fuels now escallating solar heating units have become more attractive, yet their usage is still restricted due in major part to the substantial initial expense involved in purchasing collector units.
Existing solar collectors tend to be either one of three types. Concentration type collectors localize the sun's light on a particular heat conductive member which transfers the heat to a circulating fluid which can then communicate the heat to a receptor. The labor and material expense involved in the manufacture of these focusing collectors make them impractical for many applications. In addition to the economic considerations typical concentration collectors are further limited in that they are effective for only a narrow angle of sunlight outside of which their effectiveness decreases dramatically.
Metallic pipe collectors typically include a black, fluid carrying pipe spaced between a glass or plastic cover and an insulated base. These devices often employ coiled piping or zigzagging in convolutions in a given plane requiring numerous flow restricting elbows and considerable lengths of metallic piping. Thermal inefficiencies result from the excessive spacing of the convolutions which permits radiation of much of the solar energy back into the atmosphere. Economic inefficiencies further include the excessive labor and material costs inherent in the production of the device.
The present invention is of the third variety utilizing a flat plate collector. This type system makes use of flat surfaces to absorb the solar energy, and can receive light from a wide variety of angles. Although a considerable number of flat plate collector systems exist none of these systems use the unitized mode of construction with integral fluid passageways as does the present invention. H. E. Stoutin U.S. Pat. No. 3,918,430 teaches a light weight plastic film solar collector utilizing plate collector in a plastic frame. Stout however does not disclose the use of fluid passageways integral to the plastic frame but rather requires the installation of multiple film layers and further necessitates the use of a fabricated solar ply which makes the system more expensive. In addition the use of a plastic foam insulation base in the patent results in undesirable temperature limitations of which the inventors were apparently unaware. E. W. Gough in U.S. Pat. No. 3,076,450 teaches a plastic solar heater. This patent uses a polyurethane foam plastic base which includes an undulated top that defines a series of parallel water channels. The use of a now integral frame however necessitates additional fabrication and therefore additional cost. Furthermore the application of a black plastic liner to the surface of the plastic base requires additional manufacturing and results in direct contact between the heat conducting fluid and the thin plastic liner. If such contact is continuous the result is likely to be the deterioration of the plastic liner necessitating extensive repair procedures to the replacement of the entire unit.
In the present invention heat absorption is accomplished by an absorptive coating imposed on the upper surface of the collector plate. The coating may be selective or non-selective. This construction provides for simpler assembly a more evenly distributed coating, reduces deterioration of the absorptive coating, allows much simpler maintenance when necessary and allows for more direct solar exposure upon the absorptive coating resulting in a more efficient collection system. The present invention also allows for the application of a more even absorptive coating. The construction of the integral passageways used in the present invention further allows greater surface exposure of the heat conducting fluid. This eliminates the deep troughs found in Gough and results in an overall more efficient heat transfer to the conducting fluid. The heater disclosed by Gough is also limited in that the use of polyurethane foam plastic as a heat insulator makes the system unsuitable for use at the temperatures encountered in today's solar collector systems. In applications where the low pressure of Gough does prove effective the user is left unguided in the necessary task of developing a suitable low pressure collector loop system into which it must be integrated.
In U.S. Pat. No. 2,838,043 issued to R. W. Bliss a solar water heating system is described which utilizes a high pressure self-draining heating system with a coil type collector. While the automatic draining concept disclosed by Bliss was an improvement in contemporaneous systems, it remained to be seen if a low pressure system, requiring a less stringent construction, and therefore more cost effective, could be devised which could also be self-draining and utilize a less expensive unitized mode of construction.
Although the above described systems have assisted in solving problems present in the design of an efficient solar collector, neither these nor other systems proved entirely satisfactory for the reason that no truly cost effective low pressure collector system has been proposed until the emergence of the present system.
Accordingly it is an object of the present invention to provide a new and improved solar heating system which utilizes a low pressure collector loop and a simple inexpensive collector assembly.
It is another object of the present invention to provide a durable non-corrosive solar heating system which is not easily damaged, can be manufactured at low cost, and can utilize copper plumbing.
It is also an object of the present invention to provide a self-draining solar heating system requiring minimal maintenance and suitable for high temperature operation associated with shut down.
It is also an object of this invention to provide a system for adapting a lower pressure solar heating system for use with either a high pressure or lo w pressure water heating system.
It is a further object of this invention to provide a solar collector system for preheating potable water which operates in conjunction with an existing hot water system so as not to burden the hot water system during hours of little or no sunlight.
It is a still further object of this invention to provide a solar collector system which utilizes an inexpensive molded plastic collector base which makes fluid connection, installation, interconnection of multiple units and any necessary repair relatively simple and extremely cost effective in both terms of labor and materials.
These and other objects and advantages of the invention will be apparent from the following description and claims, the novelty consisting of the feature of construction, combination of parts, the unique relations of the members and the operation thereof, all as more completely outlined herein and particularly pointed out in the appended claims.